Flexible body motions in large flexible space vehicles cause pointing disturbances for pointed instruments attached to the space vehicle. Large instrument pointing systems which torque relative to the flexible vehicle can cause structural instabilities and disturb other pointed devices. Momentum compensation methods have been used to torque pointed devices relative to rigid compensating inertias to minimize space vehicle disturbances, but these momentum compensating devices have been excessively massive or introduce pointing disturbances due to mechanism nonlinearities or mechanism rotational mass centers off the actuator rotational axis. Mass of compensating inertias can be minimized by rotating them more rapidly with the opposite polarity than the devices they compensate. The ratio of the compensating inertia angular rate to the pointed device angular rate must be kept a negative constant to assure accurate momentum compensation and device pointing. Momentum compensation methods include motor driven pointed devices with motor driven compensating inertias, or one motor driving both compensating inertia and pointed device with mechanical means such as gear mechanisms between the pointed device and compensating inertia.
Momentum compensation methods that require measurement of the pointed device and compensating inertia rotational rates do not have adequate sensors or controllers to provide the fixed rotational rate ratio required for precision pointing. To assure momentum compensation at all times, a mechanical backlash free rotational link between the pointed device and compensating inertia is desired. For these reasons a high gear ratio, single step gear mechanism with no backlash is the preferred rotational link between the pointed device and compensating inertia. The momentum compensated geared actuators to date do not have drive motor redundancy provisions because of the actuator mass penalties and backlash considerations. Accordingly, the objects of this invention are to provide a mechanical momentum compensated rotary actuator with the following features:
large single step rotational speed and polarity difference between the pointed device and compensating inertia; PA0 provisions to eliminate mechanical backlash effects between pointed device and compensating inertia; PA0 provisions to position the combined mass centers of all rotating elements on the actuator rotational axis; PA0 provisions for providing ball bearing preloads to maintain rotating element mass centers on their rotational axis; PA0 provisions to accommodate redundant actuator drive motors; PA0 provisions to minimize actuator mass penalty from addition of redundant active actuator elements.